It is known that in today's competitive sawmill environment, it is desirable to quickly process non-straight lumber so as to recover the maximum volume of cut lumber possible from a log or cant. For non-straight lumber, volume optimization means that, with reference to a fixed frame of reference, either the non-straight lumber is moved relative to a gangsaw of circular saws, or the gangsaw is moved relative to the lumber, or a combination of both, so that the saws in the gangsaw may cut an optimized non-straight path along the lumber, so-called curve-sawing.
Advances in digital processing technology and non-contact scanning technology have made possible in the present invention, an orchestrated approach to curve sawing involving a plurality of coordinated machine centers or devices for optimized curve sawing having benefits over the prior art.
A canted log, or "cant", by definition has first and second opposed cut planar faces. In the prior art, cants were fed linearly through a profiler or gang saw so as to produce at least a third planar face either approximately parallel to the center line of the cant, so called split taper sawing, or approximately parallel to one side of the cant, so called full taper sawing; or at a slope somewhere between split and full taper sawing. For straight cants, using these methods for volume recovery of the lumber can be close to optimal. However, logs often have a curvature and usually a curved log will be cut to a shorter length to minimize the loss of recovery due to this curvature. Consequently, in the prior art, various curve sawing techniques have been used to overcome this problem so that longer length lumber with higher recovery may be achieved.
Curve sawing typically uses a mechanical centering system that guides a cant into a secondary break-down machine with chipping heads or saws. This centering action results in the cant following a path very closely parallel to the center line of the cant, thus resulting in split taper chipping or sawing of the cant. Cants that are curve sawn by this technique generally produce longer, wider and stronger boards than is typically possible with a straight sawing technique where the cant has significant curvature.
Curve sawing techniques have also been applied to cut parallel to a curved face of a cant, i.e. full taper sawing. See for example Kenyan, U.S. Pat. No. 4,373,563 and Lundstrom, Canadian Patent No. 2,022,857. Both the Kenyan and Lundstrom devices use mechanical means to center the cant during curve sawing and thus disparities on the surface of the cant such as scars, knots, branch stubs and the like tend to disturb the machining operation and produce a "wave" in the cant. Also, cants subjected to these curve sawing techniques tend to have straight sections on each end of the cant. This results from the need to center the cant on more than one location through the machine. That is, when starting the cut the cant is centered by two or more centering assemblies until the cant engages anvils behind the chipping heads. When the cant has progressed to the point that the centering assemblies in front of the machine are no longer in contact, the cant is pulled through the remainder of the cut in a straight line. It has also been found that full taper curve sawing techniques, because the cut follows a line approximately parallel to the convex or concave surface of the cant, can only produce lumber that mimics these surfaces, and the shape produced may be unacceptably bowed.
Thus in the prior art, so called arc-sawing was developed. See for example U.S. Pat. Nos. 5,148,847 and 5,320,153. Arc sawing was developed to saw irregular swept cants in a radial arc. The technique employs an electronic evaluation and control unit to determine the best semi-circular arc solution to machine the cant, based, in part, on the cant profile information. Arc sawing techniques solve the mechanical centering problems encountered with curve sawing but limit the recovery possible from a cant by constraining the cut solution to a radial form.
Applicant is also aware of U.S. Pat. No. 4,373,563, U.S. Pat. No. 4,572,256, U.S. Pat. No. 4,690,188, U.S. Pat. No. 4,881,584, U.S. Pat. No. 5,320,153, U.S. Pat. No. 5,400,842 and U.S. Pat. No. 5,469,904; all designs that relate to the curve sawing of two-sided cants. Eklund, U.S. Pat. No. 4,548,247, teaches laterally translating chipping heads ahead of the gangsaws. Dutina, U.S. Pat. No. 4,599,929 teaches slewing and skewing of gangsaws for curve sawing. The 4,690,188 and 4,881,584 references teach a vertical arbor with an arching infeed having corresponding tilting saws and, in 4,881,584, non-active preset chip heads mounted to the sawbox.
Applicant is aware of U.S. Pat. No. 4,144,782 which issued to Lindstrom on Mar. 20, 1979 for a device entitled "Apparatus for Curved Sawing of Timber". Lindstrom teaches that when curve sawing a log, the log is positioned so as to feed the front end of the log into the saw with the center of the log exactly at the saw blade. In this manner the tangent of the curve line for the desired cut profile of the log extends, starting at the front end, parallel with the direction of the saw blade producing two blocks which are later dried to straighten and then re-sawn in a straight cutting gang.
It has been found that optimized lumber recovery is best obtained for most if not all cants if a unique modified polynomial cutting solution is determined for every cant. Thus for each cant a "best" curve is determined, which in some instances is merely a straight line parallel to the center line of the cant, and in other instances a complex curve that is only vaguely related to the physical surfaces of the cant.
Thus it is an object of the present invention to improve recovery of lumber from cants and in particular irregular or crooked cants by employing a "best" curve smoothing technique to produce a polynomial curve, which when modified according to machine constraints results in a unique cutting solution for each cant.
To achieve this objective, in a first embodiment, a two sided cant is positioned and accurately driven straight into an active curve sawing gang, with active chip heads directly in front of the saws, to produce the "best" curve which includes smoothing technology. In one embodiment, a machining center in the form of a profiler cuts at least a third and potentially a fourth vertical face from a cant according to an optimized curve so that the newly profiled face(s) on the cant can be accurately guided or driven into a subsequent curve sawing gang. The profiled cant reflects the "best" curve which includes smoothing technology to limit excessive angles caused by scars, knots and branch stubs; while the gang saw products reflect the previously calculated optimized cutting solution.
Due to an increased incidence of jamming of circular gang saw blades with curve sawing in general, it is another object of the present invention to orient the circular saw sawguides near the first contact point of the cant within the gang saw and still allow the sawguides to be rotated back away from the saw blades, thus allowing the saw blades to be removed more easily in the event of a cant becoming jammed than with other known curve sawing circular gang saws of the known type.